We have performed a study of the isovector, octet, and singlet axial charges of the proton in an extended chiral constituent quark model, where all the possible $uudq\overline{q}$ ($q=u$, $d$, $s$) five-quark Fock components in the proton wave function are taken into account. The ${}^3{P}_0$ quark-antiquark creation mechanism is assumed to account for the transition coupling between three- and five-quark components in proton, and the corresponding transition coupling strength is fixed by fitting the intrinsic sea flavor asymmetry $\overline{d}-\overline{u}$ data for proton. Accordingly, with all the parameters fixed by empirical values, the probabilities of the intrinsic five-quark Fock components in proton wave function should be $\sim 30–50\%$, which lead to the numerical results for quark spin $\mathrm{\Delta }u$, $\mathrm{\Delta }d$, and $\mathrm{\Delta }s$, as well the axial charges of proton consistent with the experimental data and predictions by other theoretical approaches.

Gravitational waves (GWs) from merging black holes allow for unprecedented probes of strong-field gravity. Testing gravity in this regime requires accurate predictions of gravitational waveform templates in viable extensions of general relativity. We concentrate on scalar Gauss-Bonnet gravity, one of the most compelling classes of theories appearing as the low-energy limit of quantum gravity paradigms, which introduces quadratic curvature corrections to gravity coupled to a scalar field and allows for black hole solutions with scalar charge. Focusing on inspiraling black hole binaries, we compute the leading-order corrections due to curvature nonlinearities in the GW and scalar waveforms, showing that the new contributions, beyond merely the effect of scalar field, appear at first post-Newtonian order in GWs. We provide ready-to-implement GW polarizations and phasing. Computing the GW phasing in the Fourier domain, we perform a parameter-space study to quantify the detectability of deviations from general relativity. Our results lay important foundations for future precision tests of gravity with both parametrized and theory-specific searches.

It is shown that the Cotton tensor can describe the effects of gravity beyond general relativity. Any solution of the Einstein equations with or without the cosmological constant satisfies the field equations described by the Cotton tensor. It implies that the cosmological constant is an integration constant. A vacuum of a theory is represented by the vanishing of the Cotton tensor, rather than the vanishing of the Ricci tensor. An exact Schwarzschild-like solution for a static and spherically symmetric source is discovered. Although the field equations involve the third order of derivative, it is found that they reduce to the second-order differential equations due to a variational principle.

A coarse graining technique akin to block spin transformations that groups together fiducial cells in a homogeneous and isotropic universe has been recently developed in the context of loop quantum cosmology. The key technical ingredient was an SU(1,1) group and Lie algebra structure of the physical observables as well as the use of Perelomov coherent states for SU(1,1). It was shown that the coarse graining operation is completely captured by changing group representations. Based on this result, it was subsequently shown that one can extract an explicit renormalization group flow of the loop quantum cosmology Hamiltonian operator in a simple model with dust-clock. In this paper, we continue this line of investigation and derive a coherent state path integral formulation of this quantum theory and extract an explicit expression for the renormalization-scale dependent classical Hamiltonian entering the path integral for a coarse grained description at that scale. We find corrections to the nonrenormalized Hamiltonian that are qualitatively similar to those previously investigated via canonical quantization. In particular, they are again most sensitive to small quantum numbers, showing that the large quantum number (spin) description captured by so called “effective equations” in loop quantum cosmology does not reproduce the physics of many small quantum numbers (spins). Our results have direct impact on path integral quantization in loop quantum gravity, showing that the usually taken large spin limit should be expected not to capture (without renormalization, as mostly done) the physics of many small spins that is usually assumed to be present in physically reasonable quantum states.

Treating Maxwell soft hair as a transition function that relates U(1) gauge fields living in the asymptotic region and near-horizon region, the U(1) gauge parameter $\varphi (x^a)$ naturally becomes a good label of those Maxwell soft hair degrees of freedom. This interpretation also builds the connection between Maxwell soft hair and U(1) edge modes living in the intermediate region, which admits a well-defined effective action description. We study the statistical properties by Euclidean path integral, which concludes that the soft hair density of state increases with black hole temperature. Hawking radiations increase black hole entropy by creating entanglements, while the measurements of soft modes project the black hole onto lower entropy states. The competition between phase spaces of Hawking radiations and soft hair measurements gives rise to one version of the Page curve consistent with the unitary evolution of the black hole.

Phase diagrams of the boson stars and shells of the $U(1)$ gauged $\mathbb{C}{P}^N$ nonlinear sigma model are studied. The solutions of the model exhibit both the ball- and the shell-shaped charge density depending on $N$. There appear four independent regions of the solutions which are essentially caused from the coexistence of electromagnetism and gravity. We examine several phase diagrams of the boson stars and the shells and discuss what and how the regions are emerged. A coupling with gravity allows for harboring of the charged black holes for the $Q$-shell solutions. Some solutions are strongly affected by the presence of the black holes and they allow to be smoothly connected. As a result, the regions are integrated by the harboring black holes.

The placement of a magnetic monopole into an electrically neutral chiral plasma with a nonzero axial density results in an electric polarization of the matter. The electric current produced by the chiral magnetic effect is balanced by charge diffusion and Ohmic dissipation, which generates a nontrivial charge distribution. In turn, the latter induces a separation of chiralities along the magnetic field of the monopole due to the chiral separation effect. We find the stationary states of such a system, with vanishing total electric current and stationary axial current balanced by the chiral anomaly. In this solution, the monopole becomes “dressed” with an electric charge that is proportional to the averaged chiral density of the matter—forming a chiral dyon. The interplay between the chiral effects on the one hand, and presence of magnetic field of the monopole on the other, may affect the evolution of the monopole density in the early Universe, contribute to the process of baryogenesis, and can also be instrumental for detection of relic monopoles using chiral materials.

We discuss in this paper the vacuum Cherenkov radiation in the $z=2$ Lifshitz electrodynamics. The improved ultraviolet behavior, in terms of higher spatial derivatives, and the renormalizable couplings, due to the time-space anisotropic scaling, present in the Lifshitz setting are extremely important in fulfilling the physical constraints in order to this vacuum process to happen. We evaluate in details the instantaneous rate of energy loss for a charge, and also analyze the emission of very soft photons in this framework.

We compute the vacuum fermion current in the ($2+1$) dimensional Jackiw-Rossi model by using the $1/m$ expansion. The current is expressed through a weighted $\eta$-function with a matrix weight. In the presence of such a weight, the usual proof of topological nature of $\eta (0)$ is no longer applicable. Direct computations confirm the following surprising result; the fermion number induced by vortices in the Jackiw-Rossi model is not topological.

We extend previous work on the numerical diagonalization of quantum stress tensor operators in the Minkowski vacuum state, which considered operators averaged in a finite time interval, to operators averaged in a finite spacetime region. Since real experiments occur over finite volumes and durations, physically meaningful fluctuations may be obtained from stress tensor operators averaged by compactly supported sampling functions in space and time. The direct diagonalization, via a Bogoliubov transformation, gives the eigenvalues and the probabilities of measuring those eigenvalues in the vacuum state, from which the underlying probability distribution can be constructed. For the normal-ordered square of the time derivative of a massless scalar field in a spherical cavity with finite degrees of freedom, analysis of the tails of these distributions confirms previous results based on the analytical treatment of the high moments. We find that the probability of large vacuum fluctuations is reduced when spatial averaging is included, but the tail still decreases more slowly than exponentially as the magnitude of the measured eigenvalues increases, suggesting vacuum fluctuations may not always be subdominant to thermal fluctuations and opening up the possibility of experimental observation under the right conditions.

We accurately approximate the contribution of a Yukawa-coupled fermion to the inflaton effective potential for inflationary geometries with a general first slow roll parameter $\epsilon (t)$. For $\epsilon =0$ our final result agrees with the famous computation of Candelas and Raine done long ago on the de Sitter background [P. Candelas and D. Raine, Phys. Rev. D 12, 965 (1975).], and both computations degenerate to the result of Coleman and Weinberg in the flat space limit [S. R. Coleman and E. J. Weinberg, Phys. Rev. D 7, 1888 (1973).]. Our result contains a small part that depends nonlocally on the inflationary geometry. Even in the numerically larger local part, very little of the $\epsilon$ dependence takes the form of Ricci scalars. We discuss the implications of these corrections for inflation.

This paper studies a four-field hyperbolic PDE model that was recently introduced by Bemfica, Disconzi, and Noronha for the pure radiation fluid with viscosity, and asks whether shock waves admit continuous profiles in this description. The model containing two free parameters $\mu$, $\nu$ and being causal whenever one chooses $(\mu ,\nu )$ from a certain range $\mathcal{C}\subset {\mathbb{R}}^2$, this paper shows that for any choice of $(\mu ,\nu )$ in the interior of $\mathcal{C}$, there is a dichotomy in so far as (i) shocks of sufficiently small amplitude admit profiles and (ii) certain other, thus necessarily nonsmall, shocks do not. This finding does not preclude the possibility that if one chooses $(\mu ,\nu )$ from a specific part $\mathcal{S}$ of the boundary of $\mathcal{C}$, the dichotomy disappears and all shocks have profiles; the parameter set $\mathcal{S}$ corresponds to the “sharply causal” case, in which one of the characteristic speeds of the dissipation operator is the speed of light.

In this paper, we systematically study gravitational waves (GWs) first produced by remote compact astrophysical sources and then propagating in our inhomogeneous Universe through cosmic distances, before arriving at detectors. To describe such GWs properly, we introduce three scales, $\lambda$, $L_c$, and $L$, denoting, respectively, the typical wavelength of GWs, the scale of the cosmological perturbations, and the size of the observable Universe. For GWs to be detected by the current and foreseeable detectors, the condition $\lambda \ll L_c\ll L$ holds. Then, such GWs can be approximated as high-frequency GWs and be well separated from the background ${\gamma }_{\mu \nu }$ by averaging the spacetime curvatures over a scale $\ell$, where $\lambda \ll \ell \ll L_c$, and $g_{\mu \nu }={\gamma }_{\mu \nu }+\epsilon h_{\mu \nu }$ with $h_{\mu \nu }$ denoting the GWs. In order for the backreaction of the GWs to the background spacetimes to be negligible, we must assume that $|h_{\mu \nu }|\ll 1$, in addition to the condition $\epsilon \ll 1$, which are also the conditions for the linearized Einstein field equations for $h_{\mu \nu }$ to be valid. Such studies can be significantly simplified by properly choosing gauges, such as the spatial, traceless, and Lorenz gauges. We show that these three different gauge conditions can be imposed simultaneously, even when the background is not a vacuum, as long as the high-frequency GW approximation is valid. However, to develop the formulas that can be applicable to as many cases as possible, in this paper we first write down explicitly the linearized Einstein field equations by imposing only the spatial gauge. Then, applying these formulas together with the geometrical optics approximation to such GWs, we find that they still move along null geodesics and its polarization bivector is parallel transported, even when both the cosmological scalar and tensor perturbations are present. In addition, we also calculate the gravitational integrated Sachs-Wolfe effects due to these two kinds of perturbations, whereby the dependences of the amplitude, phase, and luminosity distance of the GWs on these perturbations are read out explicitly.

Cosmic Explorer is a next-generation ground-based gravitational-wave observatory concept, envisioned to begin operation in the 2030s and expected to be capable of observing binary neutron star and black hole mergers back to the time of the first stars. Cosmic Explorer’s sensitive band will extend below 10 Hz, where the design is predominantly limited by geophysical, thermal, and quantum noises. In this work, thermal, seismic, gravity-gradient, quantum, residual gas, scattered-light, and servo-control noises are analyzed in order to motivate facility and vacuum system design requirements, potential test mass suspensions, Newtonian noise reduction strategies, improved inertial sensors, and cryogenic control requirements. Our analysis shows that, with improved technologies, Cosmic Explorer can deliver a strain sensitivity better than ${10}^{-23}{\mathrm{Hz}}^{-1/2}$ down to 5 Hz. Our work refines and extends previous analysis of the Cosmic Explorer concept and outlines the key research areas needed to make this observatory a reality.

From the amplitude analysis of the $D_s^{+}\to {\pi }^{+}{\pi }^0\eta$ decay, the BESIII Collaboration first observed the $D_s^{+}\to a_0(980{)}^{+}{\pi }^0$ and $D_s^{+}\to a_0(980{)}^0{\pi }^{+}$ decay modes, which are expected to occur through the pure $W$-annihilation processes. The measured branching fraction $\mathcal{B}[D_s^{+}\to a_0(980{)}^{+(0)}{\pi }^{0(+)},a_0(980{)}^{+(0)}\to {\pi }^{+(0)}\eta ]$ is, however, found to be larger than those of known $W$-annihilation decays by 1 order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internal $W$-conversion or external $W$-emission mechanisms instead of a $W$-annihilation mechanism. In this work, we propose that the $D_s^{+}$ decay proceeds via both the external and internal $W$-emission instead of $W$-annihilation mechanisms. In such a scenario, we perform a study of the $D_s^{+}\to {\pi }^{+}{\pi }^0\eta$ decay by taking into account the contributions from the tree diagram $D_s^{+}\to {\rho }^{+}\eta \to {\pi }^{+}{\pi }^0\eta$ and the intermediate ${\rho }^{+}\eta$ and $K^{*}\overline{K}/K{\overline{K}}^{*}$ triangle diagrams. The intermediate $a_0(980)$ state can be dynamically generated from the final state interactions of coupled $K\overline{K}$ and $\pi \eta$ channels, and it is shown that the experimental data can be described fairly well, which supports the interpretation of $a_0(980)$ as a molecular state.

We derive Kubo formulae for first-order spin hydrodynamics based on nonequilibrium statistical operators method. In first-order spin hydrodynamics, there are two new transport coefficients besides the ordinary ones appearing in first-order viscous hydrodynamics. They emerge due to the incorporation of the spin degree of freedom into fluids and the spin-orbital coupling. Zubarev’s nonequilibrium statistical operator method can be well applied to investigate these quantum effects in fluids. The Kubo formulae, based on the method of nonequilibrium statistical operators, are related to equilibrium (imaginary-time) infrared Green’s functions, and all the transport coefficients can be determined when the microscopic theory is specified.

We show that the nature of the topological fluctuations in $SU(3)$ gauge theory changes drastically at the finite temperature phase transition. Starting from temperatures right above the phase transition, topological fluctuations come in well separated lumps of unit charges that form a noninteracting ideal gas. Our analysis is based on a novel method to count not only the net topological charge but also separately the number of positively and negatively charged lumps in lattice configurations using the spectrum of the overlap Dirac operator. This enables us to determine the joint distribution of the number of positively and negatively charged topological objects, and we find this distribution to be consistent with that of an ideal gas of unit charged topological objects.

We study the photoproduction of the $\mathrm{\Lambda }(1405)$ and $\mathrm{\Sigma }(1400)$ hyperon resonances, the latter of which is not a well established state. We evaluate the $s$-, $t$-, and $u$-channel diagrams in the Born approximation by employing the effective Lagrangians. A new ingredient is the inclusion of a nucleon resonance $N^{*}(1895)$ that is dynamically generated with predictions for its coupling to the $K\mathrm{\Lambda }(1405)$ and $K\mathrm{\Sigma }(1400)$ channels. To extend the applicability of the model to energies beyond the threshold region, we consider a Regge model for the $t$-channel $K$- and $K^{*}$-exchanges. Our results are in good agreement with the CLAS data available on $\mathrm{\Lambda }(1405)$, while for $\mathrm{\Sigma }(1400)$ we predict observables for its production. We also provide polarization observables for both hyperon productions, which can be useful in future experimental investigations. The present study provides new information on the nucleon resonance $N^{*}(1895)$ which can be an alternative source for generating the hyperon resonances $\mathrm{\Lambda }(1405)$ and $\mathrm{\Sigma }(1400)$.